The relic density of the LSP, assumed here to be the
lightest neutralino, \(\tilde{\chi }^0_{1}\) , which is stable in supersymmetric SU(5) because of \(R\) -parity,
may be brought into the narrow range allowed by the Planck
satellite and other measurements [1]} via a combination of different mechanisms. It was
emphasized previously [2]} in studies of the CMSSM, NUHM1 and NUHM2 that simple
annihilations of pairs of LSPs into conventional particles would not have been
sufficient to bring the relic \(\tilde{\chi }^0_{1}\)  density down into the Planck range for values of
\(m_{\tilde{\chi }^0_{1}}\)  compatible with the LHC search limits
and other constraints on these models.
Instead, there has to be some extra mechanism for suppressing the LSP density.
Examples include enhanced, rapid annihilation through
direct-channel resonances such as \(Z, h, H/A\) . Another possibility is coannihilation with some other,
almost-degenerate sparticle species: candidates for the coannihilating species identified in
previous studies include the \(\tilde{\tau }_1, {\tilde{\mu }}, {\tilde{e}}, {\tilde{\nu }}, {\tilde{t}_1}\)  and \(\tilde{\chi }^\pm _{1}\) .
